As a brake system for a vehicle or an electronically-controlled brake system for electrically controlling a braking force of the brake system in accordance with a brake operation force, an operation amount, or the like input from a brake pedal, that is, the hydraulic pressure supplied to a wheel cylinder for driving the brake system, an ECB (Electronically Controlled Brake) for controlling a braking force by a hydraulic pressure accumulated in an accumulator is known.
In the ECB, the hydraulic pressure boosted by a pump is accumulated in the accumulator and adjusted in accordance with a brake request of the driver, and the resultant pressure is supplied to the wheel cylinder as the brake system. When the driver operates the brake pedal, a master cylinder generates a hydraulic pressure according to the operation amount. A part of the hydraulic fluid flows in a stroke simulator, and the operation amount of the brake pedal is adjusted in accordance with the pedal effort (operation force) on the brake pedal. On the other hand, a brake ECU sets a target reduction speed of the vehicle in accordance with a pedal stroke, determines distribution of braking forces to be applied to the wheels, and applies a predetermined hydraulic pressure from the accumulator to each of the wheel cylinders.
The ECB sets a proper braking hydraulic pressure according to the brake operation input from the brake pedal and supplies a proper hydraulic pressure from the accumulator to each of the wheel cylinders, thereby electrically controlling the braking force. Consequently, when a power supply unit fails, a proper hydraulic pressure cannot be supplied to the wheel cylinders. A master cut valve is therefore provided between a master cylinder and each of the wheel cylinders. When the power supply unit fails, the master cut valve is opened to apply the pressure force from the master cylinder directly to the wheel cylinders, thereby assuring the braking force.
As such a brake system for a vehicle, for example, there is one disclosed in Patent Document 1.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-225739 (U.S. Pat. No. 6,412,882 B1, Jul. 2, 2002)